I've said this on another thread and I think it applies here too, the opportunity to be successful (if you're counting success as material wealth) is open to anyone, but, it can't be open to everyone.
The opportunities aren't limitless, there are only so many highly paid, or even comfortably paid roles out there at any one time, in any sphere, to be filled. If someone leaves the top rung, and everyone moves up a rung, there's then a gap at the bottom, too many gaps at the bottom and the whole thing comes down.
And even if there were, who's going to do the lowly jobs that are needed to support these higher paid jobs? Who is a manager going to manage, if all their employees are also managers?
If I get a better paid job tomorrow, that is seen as me succeeding, my current job role doesn't become defunct because I no longer do it, someone else will need to be found to do it, with the same low pay, I'm out of the 'unsuccessful' bracket, and someone else enters into it.
On a group level, everyone being 'successful' doesn't work, those lower paid roles are needed to support the upper tiers, because without them there are no upper tiers.
Some people are either willfully or deliberately blind to this, I mean after all, who wants to think that their success is at the cost of someone else's? Of course these types of people are going to insist their hard work has got them there, and that anyone who isn't there doesn't have the work ethic or resilience they do - the alternative is to admit they're benefiting from others work.